The file system of an operating system (OS) uses a cache memory in order to speed up an accessing process to a disk device, such as a hard disk drive (HDD). For example, when data is written, the file system temporarily writes data which is requested to be written to the disk device, in a cache memory. Then, the file system asynchronously (for example, regularly) writes the data written in the cache memory in a disk of the disk device. Hereinafter, data that has been written in the cash memory will be also referred to as a “cash”
However, when an error has occurred in the disk device, the cache on the cache memory is unable to be written in the disk device, causing the cache to be lost. As a technology for coping with the loss of the cache, various technologies including the following technologies are known.
For example, a technology is known in which, when maintenance of the cache memory is performed, the data stored in the cache memory is written into another cache memory or disk device.
A technology is known in which when a single controller malfunctions, a cache data protection controller saves the data stored in the cache memory, in a cache data saving memory.
A technology is known in which when a disk control device receives a notification that power failure is detected from an uninterruptible power supply system, the disk control device stops rotation of a first disk unit and backs up data being stored in the disk cache memory in a second disk unit.
A technology is known in which a write-cache retracting area is formed in a plurality of hard disk drives in addition to a user data area, and contents of the cache memory is written in the write-cache retracting area in the case of power failure.
However, in all the technologies described above, a dedicated hardware resource is provided, separately from a hardware resource of a system which is being operated, in order to save the cache. Therefore, building and operating costs of a system are undesirably increased.
Related techniques are disclosed in, for example, Japanese Laid-Open Patent Publication No. 09-265435, Japanese Laid-Open Patent Publication No. 2008-269221, Japanese Laid-Open Patent Publication No. 2009-003789 and Japanese Laid-Open Patent Publication No. 2000-357059.